The present invention relates to an organic photosensitive member for electrophotography, and in particular, to a conductive cylindrical supporting member therefor.
A photo sensitive member for electrophotography that is used for an electrophotography device, such as a copier or printer to which electrophotography technology is applied, comprises a conductive supporting member, and a sensitive layer provided thereon and formed of an organic material containing an organic photoconductive material. The conductive supporting member is usually cylindrical for convenience of a design of the device, and the sensitive layer is coated on the outer surface thereof.
As conventional materials for the cylindrical supporting member, aluminum or its alloy having a relatively light weight and a good machinability has been used.
However, Japanese Patent Publication (KOKOKU) No. 2-17026 discloses a supporting member manufactured by an injection molding method using a material comprising a polyphenylenesulfide resin (simply referred to as PPS herein below) as a main component. The supporting member has a light weight and good chemical and thermal resistance, and is not oxidized or otherwise deteriorated in air, which is thus preferable for an organic sensitive member.
Also, Japanese Utility Model Publication (KOKAI) No. 63-54149 discloses a supporting member formed of a phenol resin, which may contain a carbon black.
However, the supporting members comprising aluminum or its alloy require individually high accurate machining to obtain a rigid dimensional accuracy (.+-.50 micrometer or less in roundness and .+-.40 micrometer in accuracy of diameter) and a preferable surface roughness (0.5-1.2 micrometer at Maximum height Rmax). Also, it requires individual machining wherein a flange for rotatably driving the sensitive member is formed, and has a disadvantage that the surface is oxidized or deteriorated due to the effect of moisture or oxygen in air. Thus, it requires to prevent deterioration, for example, formation of an anodic oxidized coat on the surface. Accordingly, it requires many steps, and costs in manufacture process.
In addition, the supporting members composed of a PPS resin as a main component have the following disadvantages. Since the volume resistivity of a PPS resin is high, that is, usually 10.sup.10 to 10.sup.13 ohm.multidot.cm, a carbon black is added to the PPS resin to provide conductivity. In the market, recently, demands on image quality and printing characteristics are getting severe. Studies for conductivity of the supporting members required to obtain good image quality and printing characteristics in practical use have revealed that the volume resistivity of the supporting member should be 10.sup.4 ohm.multidot.cm or less, and that if the volume resistivity is higher than 10.sup.5 ohm.multidot.cm, the removal of electric charges from the supporting member when the sensitive member is exposed or static electricity is eliminated from the sensitive member becomes bad, resulting in an increase in residual potential and thereby preventing good images or printed characters.
The volume resistivity of furnace carbon, which is usually used as a conductive carbon black, is 1 to 10 ohm.multidot.cm, so that more than 20 wt. % carbon black must be added to provide the supporting member with a volume resistivity of 10.sup.4 ohm.multidot.cm. However, addition of such a large quantity of carbon black increases the viscosity of the material, so that it is difficult to make it by injection-molding. Recently, a supporting member with a small diameter (about 30 mm or less in an outer diameter), a small thickness (about 3 mm or less) and a large length (several hundred mm) have been demanded, but it is very difficult to form by injection-molding.
In addition, such supporting members have a reduced mechanical strength. Thinner and longer supporting members with dimensional accuracy are more difficult to provide. The supporting members comprising a material formed of an ordinary linear-type PPS resin as a main component are affected by a slight deformation that is caused by a solution of coating liquid and heating during coating to form an organic material layer on the supporting body, so that it is difficult to obtain dimensional accuracy required for the supporting member. In addition, good chemical resistance of a PPS resin prevents the adhesion of an organic material layer to the surface of the resin during coating formation, causing frequent peeling of the sensitive layer during the use of the sensitive member, thereby resulting in a short effective life.
The present invention has been made in view of the above points, and it is a first object of the invention to provide an organic sensitive member with a cylindrical supporting member, which has a light weight, a preferable conductivity, and good chemical and thermal resistance, which can maintain dimensional accuracy despite its thin and long shape, and which is not oxidized or otherwise deteriorated in air to maintain a stable quality.
It is a second object of the invention to provide an organic sensitive member with a cylindrical supporting member that has an adequate and uniform surface roughness.
It is a third object of the invention to provide an organic sensitive member with a cylindrical supporting member that has a mechanical strength large enough to prevent deformation despite its thin and long shape.
It is a fourth object of the invention to provide an organic sensitive member with a cylindrical supporting member to which an organic material layer can adhere sufficiently during coating formation.
It is a fifth object of the invention to provide an efficient manufacturing method of the cylindrical supporting members, which has a small thickness and diameter and a large length, as described in the first, second and third objects.